1. Field of the Invention
At least one embodiment of the invention relates to the sensing of electrocardiogram (ECG) signals, in particular to the sensing of subcutaneous ECG signals.
2. Description of the Related Art
A QRS complex is a specific sequence of deflections that may be detected within an electrocardiogram (ECG) signal, measured from the body of a living being. It generally represents the depolarization of the right and left ventricles of the heart. Typically, an ECG signal shows five deflections, or waves, that are arbitrarily named P, Q, R, S and T. In an ECG signal, Q waves are generally represented as small downward deflections following the P wave, and the R wave is generally represented as a large upward deflection, or as a spike. The S wave generally represents a small downward deflection following the R wave. The time intervals between QRS complexes typically indicate the heart rate of the heart of a living being. The QRS complex of a healthy human being generally lasts for a time interval between 60 to 120 milliseconds. Wide QRS complexes, or those lasting longer than 120 milliseconds, typically indicate ventricle impairment such as bundle branch blocks. Furthermore, often, with bundle branch blocks, a second upward deflection occurs within the QRS complex. Other causes for a wide QRS complex include ectopic foci or abnormal pacemaker sites that slow conduction within the heart and increase the depolarization time of the heart muscle. Moreover, other deviations of a patients QRS complex from a normal one may indicate various symptoms for diseases or malfunctions of different parts or areas of, for example, a human heart.
It has been a central issue of cardiac research to enable precise detection, analysis, and evaluation of a patient's QRS complex. Therefore, there is a need for a method that enables a highly accurate detection of a QRS complex with an increased signal-to-noise (SNR) ratio, compared to methods disclosed within the state of the art.